Process for the preparation of high-purity magnesium hydroxide and magnesium oxide from magnesium alkoxides

ABSTRACT

There is provided a process for producing high-purity magnesium hydroxide by reaction of magnesium or reactive magnesium compounds with hydroxy compounds yielding magnesium alkoxides, followed by hydrolysis to form magnesium hydroxide, or a process for producing magnesium oxide by calcination of magnesium hydroxide.

The present invention relates to a process for producing high-puritymagnesium hydroxide and for obtaining therefrom magnesium oxide bycalcination.

Natural resources of magnesium hydroxide [CRN 1309-48-4] are rare sothat this material is seldom mined. Nowadays, magnesium hydroxide isobtained by precipitation from seawater (cf. Gilpin, W. C. and Heasman,N., Chem. Ind. (London), 1977, p. 567-572; Drum, J. C., Tangney, S.,Trans. J. Br. Ceramic Soc., 77 (1978), no. 4, p. 10-14) andprecipitation from magnesium salt solutions using calcium hydroxide.

Said manufacturing processes have one disadvantage: the magnesiumhydroxide produced in this way is hardly suitable for a large number ofcatalytic operations and for the production of special ceramics. This isprimarily due to impurities in the form of other metals making themagnesium hydroxide particularly unsuitable for catalytic processes.

DE 3 244 972-C1 discloses a continuous process for producing high-purityaluminium alcoholates. According to said publication, aluminium metal isreacted with alcohol yielding aluminium alcoholate which can beliberated from other metals present in the aluminium metal by filtrationand/or distillation because said metals are not converted or are onlyslowly converted into metal alcoholates. Up to now, however, saidprocess has not been applicable to magnesium because the magnesiumalcoholates known in the art are not liquid and, therefore, cannot befiltered.

Furthermore, they cannot be melted without undergoing decomposition and,consequently, cannot be distilled.

EP 0 244 917 describes a process for producing soluble metal alkoxidesfrom alkoxy alcohols in organic solvents, but no reference is madetherein to a process for the production of high-purity, crystallinemagnesium hydroxides having fine porosities and uniform crystallinities.

Processes for producing pure magnesium hydroxides are known in the art.For example, GB-A-667,708 suggests a three-stage process wherein thereaction is carried out with watersoluble C₁ or C₂ alcohol yieldingmagnesium alcoholate. In the second stage, said alcoholate issubstituted for a longer-chain alcohol, the C₁ or C₂ alcohol beingremoved by distillation. The resultant magnesium alcoholate is thenhydrolysed in stage 3 of said process.

The manufacture of magnesium alkoxy ethers from hydroxy ethers is knownper se (see, for instance, U.S. Pat. No. 3,657,361). However, saidpatent does not teach that high-purity magnesium hydroxides havingspecial characteristics can be obtained by hydrolysis of magnesiumalkoxy ether.

Therefore, it was the object of this invention to develop a process forproducing magnesium hydroxide having the following features:

The magnesium hydroxide produced according to the invention is requiredto have high purity, fine porosity, and uniform crystallinity.

The starting materials shall be inexpensive and readily available.

The manufacturing process shall be feasible both continuously anddiscontinuously.

Surprisingly, it has been found that the problems cited hereinabove canbe solved when employing the process described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the x-ray diffraction pattern of a magnesiumhydroxide prepared according to the present invention.

FIG. 2 is a graph showing a comparison of pore radius distribution of aprior art magnesium hydroxide and magnesium hydroxide prepared accordingto the present invention.

FIG. 3 is a graph comparing pore radius distribution of a magnesiumoxide prepared according to the present invention with prior artmagnesium oxides.

The present invention refers to a process for the continuous ordiscontinuous production of high-purity magnesium hydroxide and/ormagnesium oxide by reacting magnesium metal and reactive magnesiumcompounds with hydroxy compounds of the type R¹—A—R—OH and hydrolysingthe resultant product, optionally followed by calcination if it isdesirable to produce magnesium oxide. Optionally, the reaction isperformed using also up to 50 percent by weight alcohols of the typeR²—OH.

The hydroxy compounds to be used according to the present invention havethe general formula R¹—A—R—OH, wherein A represents an element of maingroup 6 of the periodic system (starting with oxygen) or main group 5 ofthe periodic system (starting with nitrogen). If A represents thenitrogen group, A may bear additional substituents, preferably a totalof three, for saturation of its valences. These substituents can behydrogen or an additional hydrocarbon residue R¹ which is optionallydifferent from the other ones. It is preferred that the heteroatoms A beoxygen and nitrogen, oxygen being particularly preferred.

R, R¹, and R² represent a branched or unbranched, cyclic or acyclic,saturated, unsaturated, or aromatic hydrocarbon residue having 1 to 10carbon atoms, wherein R, R¹, and R² may be different from each other andR is twofold substituted (divalent).

Preferably, R¹ is a saturated alkyl residue having 1 to 10 carbon atoms,particularly 1 to 5 carbon atoms, the alkyl residue being mostpreferably unbranched. It is preferred that R² be a branched orunbranched, cyclic or acyclic, saturated hydrocarbon residue having 4 to8 carbon atoms, the hydrocarbon residue being most preferablyunbranched, acyclic, and saturated. Preferably, R are branched orunbranched, acyclic alkylidene residues having 1 to 5 carbon atoms,unbranched hydrocarbons having 1 to 3 carbon atoms being particularlypreferred.

The instant invention is based on a process for the continuous ordiscontinuous production of liquid magnesium alkoxides by reaction ofsuitable hydroxy compounds with magnesium compounds and/or magnesiummetal which are reactive for said hydroxy compounds. For example, asuitable reactive magnesium compound is magnesium hydride. Magnesiummetal is a particularly preferred material. It was surprisingly foundthat when reacting organic compounds of type R¹—A—R—OH with magnesium orreactive magnesium compounds, the resultant magnesium alkoxides arealready liquid at room temperature.

The present invention also comprises the continuous or discontinuoushydrolysis of said liquid magnesium alkoxides, particularly magnesiumalkoxy ethers and magnesium alkoxy amines, which is carried out afterdifficultly soluble impurities have been separated, e. g. by filtration,centrifugation, or decantation, for preparing high-purity magnesiumhydroxide. After hydrolysis, there is achieved good phase separationbetween the water/magnesium hydroxide mixture and the alcoholcomponents, when compounds which are free from foreign metal ions andwhich are suitable for salting-out, particularly 0.1 to 10 percent byweight ammonium hydrogen carbonate are added to the water forhydrolysis.

The hydroxy compounds of type R¹—A—R—OH referred to hereinabove can beused alone (one compound) or as a mixture (several compounds of typeR¹—A—R—OH). Particularly if higher-viscous compounds are formed by thereaction of this invention, sedimentation of impurities which aredifficultly soluble solids is impeded. In this case, the hydroxycompounds may be used in a one- to fivefold excess in order to reducethe viscosity and thus enhance filterability. For this purpose alsoalcohols of type R²—OH can be used or can be used in larger quantities.The viscosity of the liquid/solution is most preferably adjusted bysubsequent addition of R²—OH alcohols.

Prior to or after reaction, part of the R¹—A—R—OH hydroxy compounds usedfor the reaction can be substituted for other alcohols, i. e. those ofthe R²—OH type. However, the total amount of said R²—OH alcohols mustnot be higher than 50 percent by weight, referring to the total quantityof educts and solvents to be used.

In principle, the reaction of hydroxy compounds with magnesium compoundscan also be carried out using solvents. However, use of such solventswill involve higher production cost because they must be removed afterconversion and, what is even more important, foreign solvents will havean adverse effect on the material properties of magnesium hydroxides, i.e. purity, uniform pore distribution, and crystallinity. Furthermore,when using foreign solvents, magnesium compounds often become solid andinsoluble after conversion and purification making subsequentdissolution in a nonpolar solvent necessary before the solution can besubjected to hydrolysis. When using other solvents for the reaction,amorphous magnesium hydroxides are obtained.

Magnesium alkoxy compounds which are suitable for the production ofhigh-purity magnesium hydroxide according to this invention include forexample the experimental products bis(ethylglycolato)-magnesium (VP 1),bis(n-butyl-glycolato)-magnesium (VP 2),magnesium-bis(N,N-dimethylamino-1-propanolate) (VP 3),magnesium-bis(N,N-dimethylaminoethanolate) (VP 4),magnesium-bis(2-ethylaminoethanolate) (VP 5), ormagnesium-bis(1-methoxy-2-propanolate) (VP 6).

The magnesium hydroxide produced according to this invention has highpurity. In particular, the alkali and alkaline-earth metal contentswhich have particularly unfavorable effects in catalytic applicationsare very low. The results of trace elements determinations by ICP arelisted in Table 1. For comparison, premium-grade magnesium hydroxide ofhighest purity and reagent-grade magnesium oxide, both commerciallyavailable, were included in the examinations.

TABLE 1 Trace Elements Determinations by ICP Fe Si Ti Mn Zn Ga Na CaCompound [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] Magnesium 28646 3 8 23 <5 23 9 Mg-alkoxide <2 <2 <1 <1 <2 <5 <2 Mg(OH)₂ a 12 <2 3 3<2 <5 14 6 Mg(OH)₂ b 52 699 1 7 2 <5 58 2,290 MgO c 9 51 1 6 2 4 1,375168 MgO d 15 7 3 3 <2 <5 16 10 Legend Mg-alkoxide =bis(ethylglycolato)-magnesium a = magnesium hydroxide prepared accordingto this invention b = reference substance, premium purity (manufacturer:E. Merck AG, Darmstadt) c = reference substance, reagent grade(manufacturer: Riedel de Haën AG, Hannover) d = MgO prepared accordingto this invention from Mg(OH)₂

When comparing the impurities in the magnesium metal and the impuritiesin the magnesium alkoxide compound prepared therefrom, it becomesapparent that the separation of impurities, e. g. other metals, isperformed in a highly efficient way. High-purity magnesium oxides orhydroxides within the meaning of the present invention are thoseproducts reaching the threshold values listed in Table 2.

TABLE 2 Threshold Values Fe Si Ti Mn Zn Ga Na Ca Compound [ppm] [ppm][ppm] [ppm] [ppm] [ppm] [ppm] [ppm] <50 <50 <10 <10 <10 <10 <50 <50

In particular, the threshold values listed in Table 3 characterisehigh-purity products, the low concentrations of alkali ions andalkaline-earth ions, particularly Na and Ca, being most essential andmaking said materials very useful for a large number of catalyticapplications which are very sensitive to alkali and alkaline-earthforeign ions.

TABLE 3 Threshold Values Fe Si Ti Mn Zn Ga Na Ca Compound [ppm] [ppm][ppm] [ppm] [ppm] [ppm] [ppm] [ppm] <20 <20 <5 <5 <5 <5 <20 <20

The purities shown in Table 1 can be further increased by usingbidistilled water and containers made of inert materials. When usingdeionised water for the hydrolysis, the Fe, Mn, Ti, Na, and Caconcentrations in Mg(OH)₂ (compound a) slightly increase as comparedwith the magnesium alkoxide feedstock (Mg-alkoxide).

FIG. 1 represents the X-ray diffraction pattern of magnesium hydroxideprepared according to this invention. For comparison, the diffractionpattern of the JCPDS file (no. 7-0239, Mg(OH)₂, brucite, syn) is shownas well.

Metal oxides can be obtained by calcination of the compounds preparedaccording to this invention. The compounds of this invention werecalcined in a furnace at temperatures of 550 to 1,500° C. for a periodof 3 to 24 hours. The metal oxide prepared in this way has the same highpurity as the metal hydroxide of this invention.

In Table 4 several physical data of the magnesium hydroxide preparedaccording to this invention have been compiled.

TABLE 4 Physical Data of Experimental Product VP 1 Temperature H₂O: PoreWater for of Water for Alcoholate Surface Pore Volume Radius HydrolysisHydrolysis [g/g] [m²/g] [ml/g] [Å] [pH] [° C.] 0.15:1   142 0.71¹⁾ 94 790 2:1 123 0.62¹⁾ 68 7 90 4:1 142 0.62²⁾ 88 7 90 4:1  97 0.76¹⁾ 283  190 4:1 131 0.40¹⁾ 78 4 90 Legend ¹⁾measurement by mercury porosimetry(Autopore II 9220 porosimeter, Micromeritics) ²⁾measurement by nitrogenporosimetry (ASAP 2010 porosimeter, Micromeritics)

Based on the assumption that the pore radius correlates with thecrystallite size, it becomes apparent that the desired pore radius and,thus, the desired crystallite size of the magnesium hydroxide of thisinvention can be obtained by adjusting the pH-value of the water forhydrolysis, e.g., by addition of ammonia to the water for hydrolysis.

The magnesium hydroxides and oxides of this invention have significantlynarrower and more uniform pore distributions (monomodal distributions)than conventional, commercially available products of this kind. Forcomparison, the pore distributions of magnesium hydroxide and oxide areshown in FIGS. 2 and 3. Precisely defined pore radii and narrow poredistributions have great importance in catalytic applications.

The trace impurities in the compounds of this invention were determinedby inductively coupled plasma spectroscopy (ICP), while the crystallinephases were determined by powder diffractometry. The surfaces weredetermined by the BET method, while pore volumes and radii wereadditionally determined by mercury porosimetry and nitrogen porosimetry.The compounds of this invention were calcined in a muffle furnace attemperatures of between 550° C. and 1,500° C. Deionised water was usedfor the hydrolysis.

EXAMPLE 1 Reaction with Ethyl Glycol (Stoichiometric Amounts ofCH₃—CH₂—O—CH₂—CH₂—OH); Ammoniacal Hydrolysis (VP 1)

Into a 1,000-ml three-neck flask, there were placed 20 grams of granularmagnesium to which 48.4 grams of ethyl glycol were added. The mixturewas heated. Reaction of the metal with ethyl glycol started at approx.125° C. (perceptible by the formation of hydrogen and a temperatureincrease to approx. 140° C.). Then, 100 grams of ethyl glycol were addedduring a period of 30 minutes using a dropping funnel. The liquidreaction mixture was filtered, and 100 grams of the filtrate dividedinto three aliquot portions were hydrolysed in a H₂O/alcoholate mixture(4:1) consisting of 400 grams of deionised water containing 0.2 percentby weight ammonia (T=90° C.). Hydrolysis resulted in immediate formationof white precipitate. The released alcohol was distilled off, and theresultant suspension was spray dried. The yield was equal to 98% oftheoretical.

EXAMPLE 1a Reaction with Ethyl Glycol (VP 1)

Into a 1,000-ml three-neck flask, there were placed 20 grams of granularmagnesium to which 50 grams of ethyl glycol were added. The mixture washeated. Reaction of the metal with ethyl glycol started at approx. 125°C. (perceptible by the formation of hydrogen and a temperature increaseto approx. 140° C.). Then, 236 grams of ethyl glycol were added during aperiod of 50 minutes using a dropping funnel. The reaction mixture wasfiltered, and 100 grams of the filtrate divided into three aliquotportions were hydrolysed in a H₂O/alcoholate mixture (4:1) consisting of400 grams of deionised water containing 0.2 percent by weight ammonia(T=90° C.). A white precipitate formed immediately. The released alcoholwas distilled off, and the resultant suspension was spray dried. Theyield was equal to 98% of theoretical.

EXAMPLE 2 Reaction with Ethyl Glycol and Hexanol; Ammoniacal Hydrolysis(VP 1)

Into a 1,000-ml three-neck flask, there were placed 20 grams of granularmagnesium to which 20 grams of a hexanol/ethyl glycol mixture (50:50percent by weight) were added. The mixture was heated. Reaction of themetal with the hexanol/ethyl glycol mixture started at approx. 125° C.(perceptible by the formation of hydrogen and a temperature increase toapprox. 140° C.). Then, 266 grams of the hexanol/ethyl glycol mixturewere added during a period of 50 minutes using a dropping funnel. Thereaction mixture which was still liquid at room temperature wasfiltered, and 100 grams of the filtrate divided into three aliquotportions were hydrolysed in a H₂O/alcoholate mixture (4:1) consisting of400 grams of deionised water containing 0.2 percent by weight ammonia(T=90° C.). A white precipitate formed immediately. The released alcoholwas distilled off, and the resultant suspension was spray dried. Theyield was equal to 98% of theoretical.

EXAMPLE 3 Reaction with n-Butyl Glycol (CH₃—CH₂—CH₂—CH₂—O—CH₂—CH₂—OH)Ammoniacal Hydrolysis (VP 2)

Into a 1,000-ml three-neck flask, there were placed 15 grams of granularmagnesium to which 15 grams of n-butyl glycol were added. The mixturewas heated. Reaction of the metal with n-butyl glycol started at approx.150° C. (perceptible by the formation of hydrogen). The reactiontemperature increased to approx. 180° C. Then, 252 grams of n-butylglycol were added during a period of 90 minutes using a dropping funnel.The reaction mixture was filtered, and 100 grams of the filtrate dividedinto three aliquot portions were hydrolysed in a H₂O/alcoholate mixture(4:1) consisting of 400 grams of deionised water containing 0.2 percentby weight ammonia (T=90° C.). A white precipitate formed immediately.The released alcohol was distilled off, and the resultant suspension wasspray dried. The yield was equal to 98% of theoretical.

EXAMPLE 3a Reaction with n-Butyl Glycol (Stoichiometric Amount);Hydrolysis Without Ammonia (VP 2)

Into a 1,000-ml three-neck flask, there were placed 15 grams of granularmagnesium to which 25.7 grams of n-butyl glycol were added. The mixturewas heated. Reaction of the metal with n-butyl glycol started at approx.155-160° C. (perceptible by the formation of hydrogen). Then, 120 gramsof n-butyl glycol were added during a period of 90 minutes using adropping funnel. The liquid reaction mixture was filtered, and 100 gramsof the filtrate divided into three aliquot portions were hydrolysed in aH₂O/alcoholate mixture (4:1) consisting of 400 grams of deionised water(T=90° C.). A white precipitate formed immediately. The released alcoholwas distilled off, and the resultant suspension was spray dried. Theyield was equal to 98% of theoretical.

EXAMPLE 3b Reaction with n-Butyl Glycol; Hydrolysis Without Ammonia (VP2)

Into a 1,000-ml three-neck flask, there were placed 15 grams of granularmagnesium to which 15 grams of n-butyl glycol were added. The mixturewas heated. Reaction of the metal with n-butyl glycol started at approx.155-160° C. (perceptible by the formation of hydrogen). Then, 252 gramsof n-butyl glycol were added during a period of 90 minutes using adropping funnel. The reaction mixture was filtered, and 100 grams of thefiltrate divided into three aliquot portions were hydrolysed in aH₂O/alcoholate mixture (4:1) consisting of 400 grams of deionised water(T=90° C.). A white precipitate formed immediately. The supernatantalcohol was distilled off, and the resultant suspension was spray dried.The yield was equal to 98% of theoretical.

EXAMPLE 4 Reaction with 3-Dimethylamino-1-propanol (VP 3)

Into a 1,000-ml three-neck flask, there were placed 15 grams of granularmagnesium to which 50 grams of 3-dimethylamino-1-propanol were added.The mixture was heated. Reaction of the metal with3-dimethylamino-1-propanol started at approx. 150-160° C. (perceptibleby the formation of hydrogen). Then, 197 grams of3-dimethylamino-1-propanol were added during a period of 6 hours using adropping funnel. The reaction mixture was filtered, and 100 grams of thefiltrate divided into three aliquot portions were hydrolysed in aH₂O/alcoholate mixture (4:1) consisting of 400 grams of deionised water(T=90° C.). A white precipitate formed immediately. The released alcoholwas distilled off, and the resultant suspension was spray dried. Theyield was equal to 95% of theoretical.

EXAMPLE 5 Reaction with 2-(Dimethylamino)ethanol (VP 4)

Into a 1,000-ml three-neck flask, there were placed 15 grams of granularmagnesium to which 50 grams of 2-(dimethylamino)ethanol were added. Themixture was heated. Reaction of the metal with 2-(dimethylamino)ethanolstarted at approx. 135-145° C. (perceptible by the formation ofhydrogen). Then, 321 grams of 2-(dimethylamino)ethanol were added duringa period of 5 hours using a dropping funnel. The reaction mixture wasfiltered, and 100 grams of the filtrate divided into three aliquotportions were hydrolysed in a H₂O/alcoholate mixture (4:1) consisting of400 grams of deionised water (T=90° C.). A white precipitate formedimmediately. The released alcohol was distilled off, and the resultantsuspension was spray dried. The yield was equal to 96% of theoretical.

EXAMPLE 6 Reaction with 2-Ethylamino-ethanol (VP 5)

Into a 1,000-ml three-neck flask, there were placed 15 grams of granularmagnesium to which 50 grams of 2-ethylamino-ethanol were added. Themixture was heated. Reaction of the metal with 2-ethylamino-ethanolstarted at approx. 150-160° C. (perceptible by the formation ofhydrogen). Then, 123 grams of 2-ethylamino-ethanol were added during aperiod of 4 hours using a dropping funnel. The reaction mixture wasfiltered, and 100 grams of the filtrate divided into three aliquotportions were hydrolysed in a H₂O/alcoholate mixture (4:1) consisting of400 grams of deionised water (T=90° C.). A white precipitate formedimmediately. The released alcohol was distilled off, and the resultantsuspension was spray dried. The yield was equal to 94% of theoretical.

EXAMPLE 7 Reaction with 1-(Methoxy)propan-2-ol (VP 6)

Into a 500-ml three-neck flask, there were placed 10 grams of granularmagnesium to which 15 grams of 1-(methoxy)propan-2-ol were added. Themixture was heated. Reaction of the metal with 1-(methoxy)propan-2-olstarted at approx. 120° C. (perceptible by the formation of hydrogen).Then, 59.1 grams of 1-(methoxy)propan-2-ol were added during a period of5 hours using a dropping funnel. The reaction mixture was filtered, and50 grams of the filtrate divided into three aliquot portions werehydrolysed in a H₂O/alcoholate mixture (4:1) consisting of 200 grams ofdeionised water (T=90° C.). A white precipitate formed immediately. Thereleased alcohol was distilled off, and the resultant suspension wasspray dried. The yield was equal to 80% of theoretical.

What is claimed is:
 1. A process for producing high-purity magnesiumhydroxide comprising reacting magnesium compounds metal and/or reactivemagnesium compounds with at least one hydroxy reactant having theformula: R¹—A—R—OH  (I) optionally jointly together with up to 50percent by weight of one or more alcohol reactants having the formula:R²—OH  (II) wherein (a) A represents an element of Group VIA or Group VAof the Periodic Table, wherein if A represents an element of Group VA, Acontains additional substituents selected from the group consisting ofR¹ and hydrogen; (b) R and R¹ represent a branched or unbranched, cyclicor acyclic, saturated, unsaturated, or aromatic hydrocarbon residuehaving from 1 to 10 carbon atoms, wherein R and R¹ may be different fromeach other and R is twofold substituted; and (c) R² represents abranched or unbranched, cyclic or acyclic, saturated, unsaturated, oraromatic hydrocarbon residue having from 1 to 10 carbon atoms to formdissolved magnesium alkoxides; separating less soluble impurities fromsaid liquid and/or dissolved magnesium alkoxides prior to hydrolysis;and subsequently hydrolyzing said magnesium alkoxides in the substantialabsence of solvents other than any remaining reactants to form magnesiumhydroxides containing less than 50 ppm sodium, less than 50 ppm calcium,and having a uniform pore size distribution.
 2. A process according toclaim 1, characterized in that magnesium metal is used.
 3. A processaccording to claim 1 wherein R and R¹ are branched or unbranched,saturated hydrocarbon residues having 1 to 5 carbon atoms and R and R¹may be different from each other and R is twofold substituted.
 4. Aprocess according to claim 1, wherein the hydroxy compounds of typeR¹—A—R—OH (I) are jointly reacted with up to 50 percent by weight of oneor more alcohols of the type R²—OH  (II) wherein R² represents abranched or unbranched, cyclic or acyclic, saturated, unsaturated, oraromatic hydrocarbon residue having 1 to 10 carbon atoms.
 5. A processaccording to claim 4, wherein the hydroxy compounds are employed in aone- to fivefold excess based on the stoichiometric ratio of hydroxygroups to Mg valences.
 6. A process according to any one of claims 2 and4, wherein the hydroxy compounds of formula R²—OH (II) are added notuntil after the reaction of the metal/metal compound with the hydroxycompounds of formula R¹—A—R—OH (I).
 7. A process for producinghigh-purity magnesium oxide comprising reacting magnesium metal and/orreactive magnesium compounds with at least one hydroxy reactant havingthe formula R¹—A—O—H  (I) optionally jointly together with up to 50percent by weight of one or more alcohol reactants having the formulaR²—OH  (II) wherein (a) A represents an element of group VIA or group VAof the periodic table, wherein if A represents an element of group VA, Acontains additional substituents selected from the group consisting ofR¹ and hydrogen; (b) R and R¹ represent a branched or unbranched, cyclicor acyclic, saturated, unsaturated, or aromatic hydrocarbon residuehaving 1 to 10 carbon atoms, wherein R and R¹ may be different from eachother and R is twofold substituted; and (c) R² represents a branched orunbranched, cyclic or acyclic, saturated, unsaturated, or aromatichydrocarbon residue having 1 to 10 carbon atoms to form liquid and/ordissolved magnesium alkoxides; separating less soluble impurities fromsaid magnesium alkoxides prior to hydrolysis and subsequentlyhydroxylyzing said magnesium alkoxides in the substantial absence ofsolvents, other than any remaining reactants, to form the magnesiumhydroxides containing less than 50 ppm sodium and less than 50 ppmcalcium and having a uniform pore size distribution; and calcinating theobtained magnesium hydroxides to form magnesium oxides having a uniformpore size distribution.
 8. A process according to any one of claims 1and 7, characterised in that R² represents an unbranched, acyclic, andsaturated hydrocarbon residue having 4 to 8 carbon atoms.
 9. The processof claim 1 or 7 wherein A represents an element of Group VIA of thePeriodic Table.
 10. The process of claim 1 or 7 wherein A represents anelement of Group VA of the Periodic Table.